FIX: Fixed non-normalizing eval() method in ErrorFunctions + rewritten ErrorFunction classes to prevent duplication of code.

ADD: added proggress debug output for particle swarm optimization

FIX: Removing max and min values after de-normalization of data-set, so the is_normalized() method will again return 'False' after de-normalization.

FIX: fixed an issue with NaN in GradientDescent caused by acos(x), added more debug info to errorfunction validation

ENH: Added check when DataSet constructor gets path to the file, which is not a correct DataSet archive.

ENH: Added data check before creating a new DataSet - prevents SEGFAULTs occuring when read() method was not called beforehand.

ENH: Now it's possible to specify different neuron types for different hidden layers in FullyConnectedFFNs.

ENH: Methods print_* changed for overloaded methods write_*, which make possible writing not only to STDOUT, but also to the file.